The effect of temperature on the moisture permeability of building materials

This paper presents the results of an investigation into the temperature dependence of moisture permeability for several commonly-used building materials. The experimental programme was conducted using the standard CEN Cup test method. In total, four representative materials - plasterboard, phenolic foam insulation, plywood and medium density fibreboard (MDF) - were tested at a minimum of three different temperatures. At each temperature, four relative humidity gradients were applied which enabled the variation of moisture permeability with relative humidity to be described mathematically using the concept of differential permeability. For each test condition, six samples were tested to provide adequate information for statistical analysis. Results indicate that the temperature influence on permeability is not only related to relative humidity but also depends upon the properties of the materials themselves and the proportion of liquid to vapour flow. For the plasterboard and phenolic foam insulation, the temperature effect was found to be minor. However, a significant difference in the differential permeability for the plywood and MDF was observed, particularly in the critical high humidity (liquid dominated) regime.